1. Field of the Invention
This invention relates to a finely divided silica treated with a mixture of silazanes for use in heat cured silicone elastomers.
2. Description of the Prior Art
In the silicone elastomer art, the treatment of reinforcing silica fillers is now well known as a means of preventing the reaction between the silica filler and the silicone polymer which produces "structuring" or "crepe aging" with a subsequent loss of workability of the mixture. U.S. Pat. No. 3,243,404 describes silyl amine processing aids for use in preventing the above undesirable reaction. U.S. Pat. No. 3,635,743 describes the use of a process of contacting the filler first with ammonia and then with hexamethyldisilazane.
One of the current types of curable silicone elastomer compositions comprises compositions containing both silicon-bonded hydrogen atoms and aliphatically unsaturated bonds. Recent work with this curing system has developed special formulations particularly suitable for use in low pressure molding systems where the reactive ingredients are pumped together into a mold, being mixed during or immediately preceeding the transfer process, and cured very rapidly to yield elastomeric articles. A silica filler treated as disclosed by the present invention is particularly suitable for use in compositions designed to be used in such low pressure molding systems as it imparts reinforcing of the silicone polymer without raising the viscosity of the mixture to a point where it is no longer useful in the system.